Electroreduction of carbon dioxide (CO₂) into formic acid (HCOOH) or formate can alleviate energy crises and simultaneously decrease the content of one of the main greenhouse gases. Herein, two-dimensional (2D) Bi nanosheets electrocatalyst can be obtained via in situ transformations from optimized thickness and sizes of the bismuth oxychloride (BiOCl) precursors while the precursors with improper thicknesses or sizes were electeoreduced into nanoparticles. The 2D Bi nanosheets derived from BiOCl nanoplates precursors which were synthesized with solvent of EG/H₂O (1:1) show CO₂ reduction reaction (CO₂RR) activity with high selectivity (92 % at −0.9 V vs reversible hydrogen electrode (RHE)), and high stability (15 h) with a current density of 10.5 mA cm⁻². In addition, FEs over 80 % in a wide potential window (−0.8 to −1.3 V) are obtained in an optimal range of thickness (20∼25 nm) and sizes (40∼497 nm). This work shows that the optimal thicknesses and sizes of BiOX (X = Br, Cl) nanoplates derived Bi can maintain the 2D structures and the excellent electrocatalytic activity in CO₂RR might be attributed to more exposed active sites, enhanced electrochemical active areas, and lowered contact resistance. Furthermore, the in situ transformed electrocatalysts from the BiOX precursors is a promising and general way for regulating the activity and selectivity for CO₂ reduction to formate.

将二氧化碳 (CO ₂ ) 电还原为甲酸 (HCOOH) 或甲酸盐可以缓解能源危机，同时减少一种主要温室气体的含量。在此，二维 (2D) Bi 纳米片电催化剂可以通过优化厚度和尺寸的三氯氧化铋 (BiOCl) 前驱体的原位转化而获得，而厚度或尺寸不合适的前驱体则被电还原成纳米颗粒。用 EG/H ₂ O (1:1)溶剂合成的 BiOCl 纳米片前驱体衍生的 2D Bi 纳米片显示出 CO ₂还原反应 (CO ₂RR) 活性具有高选择性（-0.9 V 时为 92 % 对可逆氢电极 (RHE)）和高稳定性（15 小时），电流密度为 10.5 mA cm ^-2。此外，在厚度（20~25 nm）和尺寸（40~497 nm）的最佳范围内，获得了在宽电位窗口（-0.8 至 -1.3 V）中超过 80% 的 FE。这项工作表明，BiOX (X = Br, Cl) 纳米片的最佳厚度和尺寸可以保持二维结构，并且在 CO ₂ RR 中优异的电催化活性可能归因于更多暴露的活性位点、增强的电化学活性区域和降低接触电阻。此外，来自 BiOX 前体的原位转化电催化剂是调节 CO ₂活性和选择性的一种有前途的通用方法。 还原为甲酸盐。